Solar water heater

Solar water heater as an alternative to natural gas

We all want to get rid of natural gas in the Netherlands but this is not without its challenges. The whole of the Netherlands is addicted to natural gas and how do you make sure that by 2030 a quarter of all homes are off gas? A good alternative for heating homes and businesses is the solar water heater.

Where solar panels provide electricity, the solar boiler provides hot water generated by solar energy and is therefore an environmentally friendly alternative to natural gas. Energy from solar boilers is an example of direct heating in contrast to solar panels, which supply electricity that later still has to be converted into heat.

From a financial and environmental point of view, an investment in solar panels is the most effective. However, a solar water heater is a good consideration in the following situations:

  • You already have solar panels on your roof and your electricity supply is therefore already green, but you also want to make your hot water environmentally friendly
  • Your roof is too small for solar panels but you do have space for solar collectors.
  • You have a nice big roof, only you can’t use it enough for solar panels because there is too much shadow on it; however, there is enough sun for solar collectors.
  • The price of gas will be taxed more heavily in the coming period in favor of the tax on electricity.
  • Your current central heating boiler needs replacing. Simultaneously install solar water heater saves money.

In these cases, a solar water heater is a good investment. But as solar panels are not only about the panels but also with inverters and power lines, the solar water heater is a term for a number of components that work together.

The components of a solar water heater

  • Solar collector and solar collectors on the roof.
  • A storage tank or water heater for storage of the heated water.
  • Pipes for cold and hot water and a water pump.
  • The combi boiler for the after-heating.

Hoe groot moet de zonneboiler zijn?

The solar collector is placed on the roof to absorb heat from the sunlight and thereby heat the liquid that runs through the solar collector. This hot water is pumped through the pipes to the storage tank where the heat is given off to the water in the tank via a heat exchanger.

The cold water is pumped back towards the collector in order to be heated again. In the summer this water is warm enough to use without additional heating. The minimum temperature for this is 60 degrees and in the summer the temperature of the water from the solar collector can reach 90 degrees Celsius!

However, in winter it is impossible to reach the minimum temperature of 60 degrees and therefore the combi boiler is used to bring the water up to temperature. This may also be necessary if the demand for hot water exceeds the volume of water present in the storage tank.

This minimum temperature is not only necessary to heat the house comfortably but also to prevent the outbreak of Legionella bacteria. Please note, there are water heaters that are only suitable for supplying hot water for showers and tap water (tap water) and there are solar water heaters that also heat the premises, the so-called solar water heater combo.

How big should the solar water heater be?

The size of the storage tank depends on the water use. And water use depends on the size and composition of the family/occupants, the size of the property and of course the behavior of the occupants.

A house with many teenagers who like to take long showers gives a completely different use than 2 residents who take short showers once a week. If you want to heat the house as well, this will obviously require more water and therefore a larger storage tank. Storage tanks are available in sizes from 80 to 300 liters and can therefore take up a lot of space.

The largest tank is almost man high. As a rule of thumb you can assume 100 liters per 2 people. And the more water that needs to be heated, the more collectors are needed. The size of an average collector is about 3 m2, which quickly fits on a roof. With a 300-liter tank, 3 collectors are soon required to heat that amount of water. If possible, install the storage tank near the combi boiler.

Not all combi boilers are suitable for post-heating. The boilers that are suitable have the Gaskeur NZ label. Where NZ stands for Solar Afterheating. These boilers are particularly suitable because they can also handle the high water temperature up to 85 degrees that the solar collector supplies to the boiler.

If you use a regular boiler in combination with a solar water heater, there is a risk of overheating. Sometimes a conversion kit is needed to connect a NZ-labelled boiler to a solar water heater. Ask your installer for more information. Solar water heater and combi boiler do not have to be of the same brand. All brands work together without any problems.

Soorten zonneboilers

Solar water heater

Types of solar water heaters

For the Netherlands, there are really only two types of interest. The boilers with the pressure-filled system and the boilers with the return system. With the first system you need antifreeze, with a return system that is not necessary.

This is because with that system, the transport fluid automatically runs back to the boiler tank when the solar water heater is out of operation. If your circumstances allow you to use a boiler with drain back system, you will be cheaper with this system because it requires less maintenance. The location of the boiler tank in relation to the collector is decisive.

Do you need a permit?

In general, you do not need a permit for a solar water heater provided you meet the requirement that the solar collector may not protrude beyond the edge of the roof and, for flat roofs, they may not be installed too close to the edge.

Also, if you have a national monument or protected city or village view, you are often required to have a permit. Informing your municipality in advance will save you from possible disappointment afterwards. Incidentally, these are the same requirements as those imposed on solar panels.

Subsidy for solar water heaters

Unlike solar panels, the national government stimulates the use of solar water heaters with the so-called ISDE subsidy. This subsidy is dependent on the size of the boiler but indicatively you can count on an amount of around € 500,- per boiler. This subsidy will only be given if the system is installed by a certified installer and if the solar water heater meets certain energy performance requirements. For all detailed information I refer you to the RVO website.

On this website of RVO you will also find the list with brands and types of solar boilers which are eligible for this subsidy including an indication of the corresponding subsidy amount. Please note that, as currently foreseen, the subsidy runs until the end of 2020.

What does a solar water heater cost?

As always, it depends on the circumstances and the size of the system. For a household, count on an investment of € 2,000 – € 4,000 in materials where the installation costs start at € 500 and can reasonably run to about a thousand euros. So if you are lucky you can pay the installation costs from the ISDE subsidy.

Although a solar water heater can be a very responsible investment, the basic rule is that nothing is cheaper than saving gas first. All the gas you don’t use is direct profit. Insulating a house properly first and then looking at buying a solar water heater is the most effective way if you want to heat your house this way. It also prevents you from buying an oversized system because the demand for heat has been reduced by the insulation.